1. Field of the Invention
This invention relates to a novel polyester copolymer and a process for the production of the same.
2. Description of the Prior Art
Polyesters, in particular, polyethylene terephthalate (hereinafter referred to as PET) has a high initial modulus of elasticity as well as excellent thermal dimension stability of widely available polymers and application thereof to tire codes has rapidly been increasing as an industrial material having severer requirements. However, a higher initial modulus of elasticity, more excellent thermal dimension stability and lower heat shrinkage are strongly required than at the present time because of providing a product with high quality, high function and high additional value and accordingly, even when using PET having excellent properties as described above, a large improvement is still required.
A number of proposals have hitherto been made concerning improvement of various properties. Of these proposals, methods of improving polyesters can be classified into the following groups:
1) Improvement on the molecular level as is found in utilization of a copolymerization reaction. PA1 2) Improvement in the molecular weight and in the core-sheath structure with a polymerized product. PA1 3) Change of conditions such as melt spinning, solution spinning, stretching, heat treatment, etc. and improvement of each of the apparatus used therefor. PA1 4) Improvement of after-working for each of the products.
Above all, the improving method 1) comprising adding an aimed improvement material in the polymerization step of the polyester will be useful for the practice on a commercial scale.
The polyester is ordinarily produced by direct esterification of an aromatic dicarboxylic acid and a diol compound by stirring and heating the mixture under some or normal pressure, or by subjecting an alkyl ester of dicarboxylic acid and a diol compound to transesterification to obtain an ester compound and low polymer and then subjecting it to polycondensation by stirring and heating the mixture in a high vacuum.
In addition to these ordinary methods, a number of proposals have hitherto been made as to improvement in the molecular level as appeared in the utilization of the above described copolymerization reaction, for example, a method comprising acetylation of the amino group of p-amino benzoic acid and then effecting the polymerization [Journal of Applied Polymer Science, Vol. 25, 1685-1694 (1980)], a method comprising adding, at the initial period of melt polycondensation of a polyester, an aromatic diamine and aromatic dicarboxylic acid or substituted derivatives and effecting the polycondensation (Japanese Patent Laid-Open Publication No. 67009/1980), and a method comprising adding, at the initial period of melt polycondensation of a polyester, an aminocarboxylic acid compound having an aromatic ring and effecting the polycondensation (Japanese Patent Laid-Open Publication No. 137217/1980). In any method, a substituted derivative of a compound having amino group is utilized from the initial period of the reaction or a compound having amino group is added at the initial period of melt polycondensation of a polyester.
In the utilization of a copolymerization reaction for the improvement on molecular level, a segment for the improvement can be incorporated in a host molecular chain and it is thus possible to choose the variety of an additive and the copolymerization proportion according to the object of the improvement, for example, the thermal dimension stability, heat shrinkage, initial modulus of elasticity, elongation, toughness, etc. of a molded article of the copolymer.
The means for incorporating an aromatic compound having an amino group into a polyester molecular chain according to the present invention is based on this consideration relating to designing on a molecular level.
Since the aimed-improvement can be accomplished by designing on a molecular level according to this means, as described above, a number of proposals have hitherto been made, but there arise problems in these proposals that in the case of a copolymerization reaction of an aromatic compound having an amino group with a polyester-forming compound, having been proposed up to the present time, a substituted derivative is once formed, for example, by acetylation before the copolymerization reaction and then subjected to the copolymerization reaction, thus resulting in increase of the costs for raw materials and for installation of reaction vessels before the existing polyester reaction process. In addition, in the case of adding an aromatic compound having amino group at the initial period of melt polycondensation, there arises a problem that the existing polyester reaction process must be improved, for example, by installing a conduit for introducing an aromatic compound having an amino group at the late period of the esterification reaction or transesterification reaction or by installing a conduit provided with a means for preventing vacuum leakage, in particular, in the case of adding an aromatic compound having an amino group at the initial period of a polycondensation when the reaction proceeds in vacuum. Anyway, it is essential to install a new introduction conduit in the existing process.